For the synthesis of ozone molecules energy is necessary which can be provided by photons or electrons. The apparatus using photons for O.sub.3 synthesis are ultra-violet lamps, X-ray equipment or chemico-nuclear reactors. The present apparatus in which electrons are used for O.sub.3 synthesis generates alternating-current or direct-current discharge coronas. Hitherto, there has been only one viable utilization of the direct-current discharge corona, namely as disclosed in applicant's co-pending application Ser. No. 717,190 filed on Aug. 24, 1976, now U.S. Pat. No. 4,062,748.
Alternating-current corona instruments to produce ozone have been known since the beginning of this centry by the name "Siemens ozonisers". The basic principle of these alternating-current ozonisers is the known alternating-current corona which is generated in the space between the electrodes covered with dielectrics. Ozonisers with plate electrodes or tubular electrodes are based on this principle. In "Siemens ozonisers" the use of a dielectric is absolutely essential for generating the alternating-current corona. It has not been possible heretofore to generate an alternating-current corona without the said dielectric. Joule's heat which has to be dissipated from the ozoniser by cooling is produced in the dielectric. Further, the Siemens ozoniser requires dry gas in the space between the electrodes. Water has to be extracted from the oxygen-containing gas down to 0.01 g of H.sub.2 O per m.sup.3, which corresponds to a dew point of approximately -60.degree. C. It is impossible to generate an alternating-current corona if the humidity of the gas is at e.g. a dew point of +20.degree. C., which corresponds to 17.5 g of H.sub.2 O per m.sup. 3. The problem of the invention is to create a device for the production of ozone, namely on the basis of an alternating-current high voltage, excluding a dielectric, cooling of the device and prior dehydration of the oxygen-containing gas for conversion into ozone.
This problem is solved with a device of the above-mentioned type by the fact that there are arranged spaced and standing opposite one another in the discharge tube whose walls consist of electrically-non-conductive material, two plate electrodes which are connected to an alternating-current high-voltage source and/or high-voltage source for pulsating direct current and between which at least one bipolar electrode is arranged free of current connection.
This solution is based on the following:
Atmospheric air or oxygen is partly ionised by cosmic radiation or by ultra-violet radiation from the sun. When such partly ionised air flows through the discharge tube of the device and when alternating-current voltage oscillates between the electrodes, the ions migrate by the known "skin effect" from the center of the discharge tube between the electrodes to its walls where a thin layer of electrically charged gas molecules or gas atoms accumulates. This layer is two to three times more electrically conductive than the total gas in the discharge tube.
On a further increase in the voltage, current begins to flow on the surface through the thin layer of ions, i.e., an alternating-current corona is generated which, in turn, generates many more ions from the molecular gas. These ions continue to collect by skin effect on the walls of the discharge tube. The alternating-current of the corona (in the order of milliamperes) along the walls of the discharge tube can be controlled by the adjustable alternating-current voltage.
If, on the other hand, a direct-current voltage is generated between the electrodes, no current at all flows between the electrodes and thus none either on the walls and none either between the plate electrodes.
When direct current flows through a homogeneous conductor the current distribution through the cross section is homogeneous, hence uniform. In the case of alternating-current or pulsating direct-current, the density of the current is displaced to the surface of the conductor. This "skin effect" is utilized in the solution according to the invention, thereby presenting the following advantages:
The arrangement of a dielectric is superfluous and Joule's heat which otherwise occurs does not have to be dissipated. At the relatively low temperature of the alternating-current corona no nitrous gases arise.
The device according to the invention requires no pre-dried air and consequently no additional energy.
In comparison with the device in the above-referenced co-pending application Ser. No. 717,190 there are, besides, the following advantages:
The electrodes and bipolar electrodes do not need any discharge points and an alternating-current transformer is used which is less expensive than a direct-current generator. The alternating-current corona starts at a substantially lower voltage than does a direct-current corona, i.e., the voltage of the alternating-current corona lies between 5,000 and 40,000, i.e., it is controllable within a range of 35,000 volts. The direct-current corona on the device according to applicant's co-pending application Ser. No. 717,190 has a voltage of 25,000 to 40,000 volts, i.e., twice as narrow a control range is present therewith as with the alternating-current corona. The breadth of the controllable voltage of the corona is of importance for the electronic control of the ozoniser.
A further important advantage of the present device over that according to applicant's co-pending application Ser. No. 717,190 lies in the fact that with this alternating-current corona many more bipolar electrodes can be used than with the direct-current corona and, therefore, the ozone yield in g/kWh is even larger than that indeed obtained on the device operated by direct current in comparison with the known state of the art.
The device according to the invention is explained below with reference to the accompanying drawing.